Calcium phosphate such as hydroxyapatite is widely used as a biocompatible material in a medical field.
It is expected that, in particular, a complex material prepared by coating a surface of a substrate with calcium phosphate is applied to a percutaneous device such as a catheter, because such a complex material has a high cell adhesion. For example, there has been proposed a technique to use, for a percutaneous device, a complex material prepared by bonding fine particles of calcium phosphate to a surface of a flexible polymer substrate made of, for example, silk fibroin (e.g. Patent Literatures 1 and 2).
Patent Literatures 1 and 2 disclose, as a method for coating a surface of a substrate with calcium phosphate, a method for bonding calcium phosphate particles to the surface of the substrate by giving a functional group to the surface of the substrate. More specifically, after a surface of silk fibroin is treated first with a radical initiator such as hydrogen peroxide solution or ammonium persulfate (APS), a silane coupling agent is graft-polymerized onto the surface of the substrate. Thereby, the functional group is introduced onto the substrate. Then, the functional group and calcium phosphate are bonded and thereby, the substrate is coated with calcium phosphate.
Patent Literature 3 discloses a method for fixing hydroxyapatite on a surface of a substrate by immersing, into calcium solution, the substrate having been surface-treated by corona discharge treatment and plasma treatment. Apart from a purpose of bonding calcium phosphate, ozone treatment, ultraviolet irradiation, or the like is known as a method for treating a surface of a substrate (e.g. Patent Literatures 4 to 6)